Multiple myeloma (MM) is a bone marrow cancer in which a single plasma cell clone has turned malignant and produces monoclonal immunoglobulin (Ig). MM patients have a very poor prognosis. Although high response rates and increased survival can be achieved using high dose chemotherapy followed by autologous or allogeneic stem cell grafting, the majority of patients relapse and few, if any, are cured.
Myeloma cells produce monoclonal Ig that is unique for each tumor and thus for each individual patient. Ig is composed of two identical heavy (H) and two identical light (L) chains. L and H chains have highly diversified variable (V) regions, VL and VH. VL and VH together form the Fv (fragment variable) that contains unique antigenic determinants called idiotopes (Id). Idiotopes collectively constitute the idiotype of the Fv (of the Ig in casu). Induction of an immune response against the idiotype, so called Id-vaccination is a promising strategy in treatment of B cell lymphomas and MM (Bendandi, Gocke et al. 1999) (Tao and Levy 1993) (Huang, Wu et al. 2004) (Hakim, Levy et al. 1996) (King, Spellerberg et al. 1998) (Biragyn, Tani et al. 1999; Biragyn, Ruffini et al. 2002), and both anti-idiotypic antibodies (Sirisinha and Eisen 1971; Hough, Eady et al. 1976) and Id-specific T cells (Lauritzsen, Weiss et al. 1994) may be of importance. However, Id is a weak self-Ag in its original context (as part of Ig). Therefore, for vaccine purposes, it is important to enhance the immunogenicity of Id.
T helper cells (CD4+ T cells) recognize their antigen (Ag) after it has been processed through engulfment of foreign proteins by APC, proteolytic breakdown into peptide fragments that are loaded onto MHC class II molecules and transported to the surface of the APC where the peptide-MHC complex is presented to T cell receptors (TCRs) of CD4+ T cells. Activated CD4+ T cells stimulate cytotoxic T cells (CD8+ T cells) and B cells with the corresponding Ag specificity, initiating a broad response against the original Ag. A major problem concerning Id-vaccination of MM patients is that Id-specific CD4+ T cells in these patients, as extrapolated from experiments in mice [18], probably are tolerant to Id V-region determinants on the highly abundant myeloma protein. MM patients who have undergone autologous stem cell transplantation (ASCT) may be in an advantageous phase for Id-vaccination for the following two reasons: 1) relief from T cell tolerance to myeloma protein Id and 2) development of new T cells that can respond to Id-vaccination.
Targeting of T cell epitopes to surface molecules on APC with Troybodies (Lunde, Munthe et al. 1999), which are equipped with a T cell epitope incorporated in a loop in a constant Ig domain results in increased T cell stimulation by a factor of 100-100000 (Lunde, Rasmussen et al. 2001). However, Troybodies do not include the Ag in its native conformation, such as Fv, and are therefore restricted to induction of T cell responses. Therefore, to induce an anti-Id B cell response and anti-Id Abs, it is necessary to include the complete Fv of the M component of the patient. As for induction of an anti-Id T cell response, an inclusion of the entire Fv will greatly increase the chance of including idiotope sequences binding the patient's HLA-molecules, which is a prerequisite for activation of Id-specific T cells.
There have been several approaches for rendering idiotypes more immunogenic. Protein vaccination with complete Id+ immunoglobulins (Ig) fused with granulocyte-macrophage colony-stimulating factor (GM-CSF) (Tao and Levy 1993), or CD40 ligand (Huang, Wu et al. 2004) enhances the level of anti-Id antibodies and results in protection against B-cell lymphoma in mice. However, scFv-GM-CSF was effective only when injected as protein and not as a DNA vaccine (Hakim, Levy et al. 1996). On the other hand, DNA vaccination employing scFv fused to IL-1β did induce tumor immunity (Hakim, Levy et al. 1996). In another approach, scFv has been genetically fused with fragment C from tetanus toxin and delivered as a DNA vaccine by intramuscular (i.m.) injection. This strategy has resulted in increased levels of anti-Id antibodies, Id-specific CD4+ responses and protection against lymphoma a myelomas in mice. The mechanism of adjuvant activity of tetanus toxoid fragment C is unknown (King, Spellerberg et al. 1998). In a similar approach, scFv has been fused to chemokines like MCP3, IP10 mDF2β (Biragyn, Tani et al. 1999; Biragyn, Ruffini et al. 2002) and has been used both as a DNA and as protein vaccine (Biragyn, Tani et al. 1999). In several of these studies, foreign T cell epitopes corresponding to TT fragment-C or unique fusion sequences could have contributed to responses. Heightened anti-Id antibody responses and tumor protection has been observed. The mechanism of action of scFv-chemokine is unknown. One possibility is that the chemokine moiety targets Fv to chemokine receptors on APC for enhanced delivery of scFv. Alternatively, chemokines attract APC to the site of injection. However, both the Fragment C and chemokine fusion strategies rely on monovalent binding to their target molecules (King, Spellerberg et al. 1998; Biragyn, Tani et al. 1999). This is of concern because crosslinking has been shown to be of importance for optimal stimulation of T cells, e.g. for Troybodies (Lunde, Munthe et al. 1999).
With these considerations in mind, the inventors have designed a novel type of recombinant antibody-like molecules called Vaccibodies, a divalent molecule comprising a flexible hinge, with no FcR binding and that contain the Ag in its native conformation, with the purpose of inducing both strong Id-specific Ab and T cell responses. Vaccibodies are large and complex macromolecules, but, surprisingly, cells were able to produce and export intact molecules.